Comparison of Landsat-7 ETM+ and ASTER NDVI measurements

The quantitative relationship between the Normalised difference Vegetation Index (NDVI) data of Landsat and ASTER sensors has not yet been examined though they have been frequently used in medium-scale vegetation observations. To meet this need, this paper investigated the relationship of the NDVI measurements between Landsat-7 ETM+ and ASTER. The study examined how well ASTER sensor vegetation observations replicate ETM+ vegetation observations, and more importantly, the differences between the two sensors in the NDVI-based vegetation observations. Three date-coincident image pairs of the two sensors were used in this comparison study. The digital numbers of the image pairs were converted to at-satellite reflectance. The regression analysis of the scatterplots of ETM+ NDVI versus ASTER NDVI was carried out to reveal their quantitative relationship. The model for the conversion of NDVI data between the two sensors was also obtained by the regression. The results show that there are differences between the NDVI data of the two sensors despite a very strong positive linear relationship between them. The ASTER sensor generally produces lower NDVI measurements than ETM+.